In recent years considerable interest has centered on lung water homeostasis and in particular on the movement of fluid and solutes across the alveolar-capillary interface. The alveolar epithelium plays a significant role in this process as a major barrier to fluid and solute movement and as a source of active ion transport from the alveolar subphase to the interstitium. Research proposed in this application will determine the properties of active transport for alveolar type II monolayers and their characteristics as a barrier. These studies will utilize techniques developed in our laboratory to isolate alveolar type II cells from both rat and human lungs and culture them on collagen coated filters. Specific questions to be answered will include whether sodium is the sole ion responsible for the amiloride sensitive short circuit current, the role of other ions in active transport, and the associated movement of water. In addition, permeability and active transport characteristics will also be determined for monolayers grown on other supportive substrates (i.e. an extracellular matrix and human amniotic basement membrane) which may more closely approximate the connective tissue matrix in vivo. A variety of agents can injure the alveolar epithelium and create permeability defects in vivo. In order to better understand the nature of these permeability defects and the mechanisms by which they are created, I will examine the permeability alterations produced by oxygen metabolites and neutrophil proteases on alveolar type II monolayers. Particular attention will be placed on assessing the cellular defenses and recovery capabilities of these monolayers. Thus, with the completion of this project we should have a better understanding of the role of the alveolar epithelium in normal lung-water homeostasis, the mechanism by which specific etiologic agents may alter the alveolar epithelium and produce pulmonary edema, and the alveolar epithelium's role in the resolution of pulmonary edema.